It all started with the melting of the glaciers, which caused a huge landslide in Greenland in September last year, causing a mega-tsunami of about 200 meters. Then something inexplicable happened - our planet was shaken by a mysterious tremor for 9 days.

Dozens of scientists around the world tried to find out what happened. Now they have come up with an answer and warn that the Arctic is entering "uncharted waters" due to climate change.

When seismologists began recording unusual, long tremors last September, they thought it might be an instrument malfunction.

“Actually, it wasn't the rich orchestra of high notes and rumbles you'd expect from an earthquake, but more of a monotonous rumble. Earthquake signals last for a few minutes, and this one lasted for nine days. We were baffled, we had never seen anything like this before," seismologist Stephen Hicks of University College London told CNN.

Seismologists traced the signal to East Greenland but could not pinpoint the source, so they contacted colleagues in Denmark who had received reports of a tsunami following a landslide in the Dickson Fjord region.

After that, there was a year-long collaboration between 68 scientists from 15 countries, who, in order to solve the puzzle, analyzed in detail all possible seismic and satellite data, as well as simulations of tsunami waves.

"There is a so-called cascade risk, and it all started with human-caused climate change," said Danish seismologist Kristian Svennevig.

At the base of a large mountain that rises 1200 meters above Dixon Fjord, there is a glacier that has been slowly melting for years.

As the glacier shrank, the mountain became increasingly unstable, before collapsing on September 16 last year. In the process, enough rocks and debris fell into the water to fill 10 Olympic swimming pools.

A mega-tsunami ensued, one of the largest in recent history, and set off a wave that remained trapped in the narrow fjord for more than a week, splashing back and forth every 90 seconds. In doing so, vibrations were felt across the planet; the signal traveled from Greenland to Antarctica in about an hour.

The phenomenon refers to the rhythmic movement of the wave in an enclosed space, as when water moves back and forth in a tub or cup. Although we already knew about this phenomenon, scientists did not know that it could last so long.

"If I had said a year ago that a phenomenon could last nine days, my colleagues would have shook their heads and said it was impossible," says Svennevig.

Fortunately, no one was injured during the mega-tsunami, although it destroyed centuries-old cultural heritage and damaged an empty military base. But this is an area on the cruise ship route, and if any of them had been there at the time of the tsunami, the consequences would have been catastrophic.

"East Greenland has never had landslides and tsunamis like this before," Svennevig said. As the Arctic warms, mega-tsunamis may occur more frequently. In June 2017, four people died in the tsunami in northwest Greenland.

"Natural phenomena are starting to be unusual, which shows how the world is changing. This is a sign that climate change is pushing natural systems into uncharted waters," Svennevig said.

The research "A tsunami generated by a rockslide in a Greenland fjord fell to Earth in 9 days" was published in the journal Science.